Rationally Speaking #1 - Why be rational?

Why is "speaking rationally" a worthwhile goal anyway? It's not self-evident, at least not to many people. Human beings certainly don't seem made for it. Aristotle may have famously dubbed us "the rational animal," but cognitive science tells a different story, with plenty of evidence that our brains blithely flout logic all the time and are excellent at rationalizing our irrational decisions after the fact. Indeed, it is reasonable to ask why fight our irrational natures to begin with? After all, some argue that irrationality can make us happier, at least in certain situations. Then again, perhaps there is a problem with the whole idea of arguing for irrationality...